1. Field of the Invention
The present invention illustrates a power converter, and more particularly, a bi-directional power converter for converting power between an alternating current and a direct current.
2. Description of the Prior Art
With advancement of techniques, various electronic devices having different driving power requirements are adopted in our daily life. Some electronic devices require a direct current to drive functions. For example, a smart phone or a notebook generally uses the direct current generated from their batteries for driving functions. Some electronic devices require an alternating current to drive functions. For example, a television or a refrigerator uses the alternating current for driving functions. Actually, many electric appliances have alternating current plugs. A user can insert an alternating current plug into a socket. Then, the electric appliance can connect to an electrical grid for draining the alternating current. Specifically, the alternating current is an electric current in which the flow of electric charges periodically reverses direction. Generally, the waveform of alternating current inmost electric power circuits is a sine wave. Thus, the alternating current is typically used for power transmission or power driving at a high frequency. Particularly, the direct current is the unidirectional flow of electric charges. In other words, the direct current flows in a constant direction. The direct current can be produced by power sources such as batteries, power supplies, thermocouples, solar cells, or dynamos.
To improve operation convenience, some power converters can output the direct current from the alternating current. For example, a battery charger can be used for converting the alternating current from the electrical grid to the direct current in order to charge a lithium battery in the smart phone. A power inverter can be used for converting the direct current to the alternating current. For example, solar power plants can generate direct currents by using the solar energy. Then, the solar power plants can be connected to the power inverter for outputting alternating currents which can be generally used for common electric appliances.
However, aforementioned power converters are categorized as unidirectional power converters. When a power converter is designed as a bi-directional power converter, it is required that an intact circuit of power charger and an intact circuit of power inverter are combined in conjunction with a switch for selecting to drive the power charger circuit or the power inverter circuit. Since the conventional bi-directional power converter requires the intact circuit of power charger and the intact circuit of power inverter, a circuit size of the conventional bi-directional power converter cannot be reduced. Further, since the conventional bi-directional power converter may perform asymmetric input/output power conversion, the conventional bi-directional power converter may waste additional power.